The current invention provides a watertight flashlight with an adjustable intensity that finds application for a wide variety of uses such as scuba divers, auto mechanics and soldiers. Prior art provides a flashlight with a rotary switch offering "ON" and "OFF" positions. It does not provide a momentary "ON" position. The prior art switch is not easily accessible by the thumb of a user. It does riot provide a variety of output light modes. The activator or switch is not easily visible to a user making it difficult for a user to know its mode. The prior art design does not provide a means to continuously vary the intensity of the emitted light within a range of intensities. Prior art provides a watertight design with a seal at the switch but no disclosure is made regarding the ability of the prior art seal to release the internal hydrogen gas from its case to avoid a safety hazard. The switch on the prior art design does not include a means to lockout movement to prevent accidental switch activation. The contacts for the switch are part of the case. Therefore, worn or pitted contacts are not easily replaced if they become corroded. Prior art does not provide a means for the lens to assume control of the intensity of the lamp thereby permitting a user with large gloves to operate the light. Prior art does not provide a means to permit the position of the lens to limit the intensity of the emitted light.